Hull or body of craft



AprilZl, 1931. F. MELCHER HULL OR BODY OF CRAFT Filed May 29, 1930Patented Apr. 21, 1931 PATENT @FFlC'E r nan'z Marianna, on VIENNA, Ausralia HULL 0R BODY OF CRAFT Application filed. May 29, 1930, Serial No.457,143, and in Austria May 3, 1927.

This invention relates to an improved hull or body for wateror aircraftwith lateral propelling screws, and consists in the provision on thesaid hull or body of stream- '5 line furrowed guiding members of acertain definite construction, which are built into or applied to thesaid hull or body in a certain position in regard to the propellingscrews, and are designed to influence and to regulate the flow of themedium concerned up to and past the said screws. Y

The contours of a ships hull as alsothe constructional appendages suchas frollchecking fins or bilge keels, stem-shaft bosses, and the likepertaining thereto influence the flow of the water to the screws merelyas an expedient for enabling, especial- 30 ly in connection withshallow-draught river craft, the largest possible propellers to beemployed; the degree of propelling efficiency in the case of all suchdesigns is unfavourable,

since the flow to the propeller is impeded. in the furrowed hull designshitherto made known the depressions provided are directed downward sothat the screwwater is brought I to the screw mainly from below, whichimplies an increase in the consumption of power; moreover these de)ressions or hollows are seldom designed in accordance with correctstream-line principles.

The above-mentioned bottom screw-tubes and the lateral or other recessesin the V cinity of the propellers are deleterious to the propellingeficiency in addition to increasing the resistance of the ship, forwhich reason their employment has been generally abandoned in navalarchitecture and is only resorted to in particular exceptional cases.

for shallow-draught vessels. Attempts have also been made to employlongitudinal guid-.

ing channels or furrows of cylindrical crosssection and with a lateralslot or opening for the accommodation of propellers, but these againhave proved to lead to a disproportionate increase in the resistance ofthe ship. The unfavourable effect of all these hitherto known expedientsis also in part due to the unevenness set up thereby in the flow of thepropeller stream and inthe freeing of the tailavater, which in its turngives rise to the formation of eddies and to the increase of the thrustdeduction. The proposal has also been made to apply longitudinallyfinlike excrescenoes to the hull or body of Water and aircraft in frontof the propeller for the purpose of influencing the flow; in this case,however, the sharp longitudinal edge give rise to disturbing eddieswhich increase the resistance of'the ship. Appendagts of his nature ashitherto proposed are not adapted to the natural conditions of flow, andcan therefore give rise to disturbances in connection with thefreeing'of the stream from 75 the hull. Y Further the incorporation ofjspecial jet-shaped guiding-members of restricted length for theguidance of the propeller stream has also been proposed, but; these alsoproduce a disproportionate increase in re-. sistance. I I

A truly efiective guidance of the propeller stream is not ensured by anyof the manifold constructional proposals hitherto made in thisdirection. 8;";

The present invention has for its object to provide, primarily inconnection with multiple-screw and especially twin-screw ships oraircraft, longitudinal gliding furrows disposed in the range of the flowto and'from the propelling member and of a particular design calculatedto guide the screw-jet as unobstructedly as possible and to isolate thesame as far as possible from the disturbing influa ence of the adjacentstructural portions or appendages of the ships hull, independently ofthe, trim of the latter, and thus to reduce the thrust deduction(resistance to the indraft or suction of the propeller, the so calledthrust deduction) and to increase the degree of propelling efliciency. Afurther object of the invention is so to construct that portion of thehull of the water or airship which is most exposed to the impact of thepropeller stream that the liquid particles travel through the shortestpossible course to and from the propeller along the ships hull, wherebythe vertical stream component is reduced to a minimum. 7

An example of the embodiment of the invention in a. ship with twolateral stern propelling screws is shown in the accompanying drawings,in which Fig. 1 shows in side elevation the portion of the ships hullconcerned, while Figs. 2, 8, and l are transverse sections on the ines aa, b b, 0-0 respectively of Fi. 1.

T he side walls 1 of the hull are provided in the region of thepropelling screw 2 with longitmflinel furror-Js 5 which serve for theguidance of the propeller stream. Each of these guiding furrows 8 isconstituted by the fiormation (.11 or application to the ships hull ofexcrescences l which proj ct slightly beyond the mean girth of the shipand are provided with a very gradual transition into the sides of thehull, so that the re stance of the ship is not appreciably increasedthereby.

The profile of the inner surface of the furrow or depression thus formedbecomes gradually shallower and broader towards both ends away from thepropeller in accordance with the reduction in the cross-section of thescrew-jet in the vicinity of the propeller. The distance between theresulting areshaped longitudi: al ridges 5 thus increases gradually fromthe position occupied by the propeller towards each end of the furrow.These longitudinal ridges must as nearly as possible follow orthogonaltrajectories.

It is advisable to employ the excrescences forming the guiding furrowsto encae as much as possible of the propeller-shaft supports 6 (see Fig.3) and of any other auxiliary structural parts included in the design;any longitudinally disposed structural members of the hull or body, suchas roll checking fins 7, shaft boss fins or the like, (see Fig. 2) areso placed and constructed that their contours gradually merge into thoseof the excrescences.

T he profile of the guiding furrow in crosssection is a varying arewhich in the immediate vicinity of the propeller is concentric to theshaftofthc latter. Forward and astern of the propeller this profile isflattened out gradually and finally passes intothatofthe skin of thehull. The breadth of the furrows is also reduced from the ends towardsthe propeller in accordance with the gradual acceleration of thepropeller stream up to the propeller and with the deceleration of thescrew-jet after the propeller, and is least in the region of thegreatest constriction of the screw-jet behind the propeller. Thedescribed method of con.- struction has the effect of deflecting thepropeller stream gradually, and without in any way disturbing orcounteracting the natural. flow, into the direction of the axis of thepropeller before the latter is reached. The screw-jet is directedunobstructedly into comparatively quiet water.

hen the distance from the propeller to the stern-post 11 is relativelyslight the excrescences forming the guiding furrows can be tapered offat the stern ends by the hollowing-in of the transitional surfaces 9 and10 between the excrescence proper and the hull skin to form sharp edges12, whereby the danger of the development of any drag effect at thesepoints is eliminated.

The described means are capable of i11- creasing to a considerableextent the propelling effieiency of ships of every kind, and inparticular of such as are provided with latoral stern propelling screws.

Guiding surfaces or furrows constructed on the same principle can alsobe used in aircraft within the range of the propeller current. No usehas hitherto been made at all of guiding furrows for the propellercurrent in this connection.

I claim 1. In the hull of a ship of the type having lateral propellingscrews, guiding furrows with restricted portions formed by excrescenceson the said hull following orthogonal trajectories, said excresccncesbeing adapted to project slightly beyond the mean girth of the said shipin such a manner that the cross-section of the said furrow exhibits thegreatest curvature adjacent the position of the greatest constriction ofthe screw-jet and becomes gradually wider and shallower towards bothends of the said furrow, for the purpose of causing the water flowingtowards the said propeller to be gradually and without violencedeflected into an axial direction before entering the said propeller.

2. A hull or body as in claim 1, in which said excrescences encase screwshaft supports of the hull or body at the base of said shafts and withinand by the excrescences.

3. A hull or body as in claim 1 in vhich the stern end of theexcrescences form a sharp edge.

In testimony whereof I have signed my name to this specification. H

FRANZ MELCHER.

